When you carry extra pounds you also speed up the loss of cartilage in your knees. That's the stuff that creates a cushion between your bones. If you don't have enough, your bones start to rub against each other. And that leads to irritation, pain, and swelling.
When you drop a few pounds, you won't reverse your OA or create new cartilage. But it can ease your symptoms, improve how well you get around, and prevent more damage to your joints.